Closed loop fuel control systems are commonly used in gasoline-powered vehicles to maintain an operating air-fuel (A/F) ratio at stoichiometry. Stoichiometric values, however, can vary with fuel composition. For example, when fuel is added to a vehicle fuel tank, it mixes with fuel already in the tank. For example, ethanol or gasohol in varying mixtures can be added to gasoline already in the tank. If the added fuel has a different composition from that of the fuel already in the tank, the engine of the vehicle may operate at a different stoichiometric value after the refueling. Currently manufactured vehicles may include a hardware sensor that senses and communicates ethanol content in fuel to other systems in the vehicle.